Wireless base stations are well known in the art and typically include, among other things, baseband equipment, radios and antennas. The antennas are often mounted at the top of a tower or other elevated structure, such as a pole, a rooftop, water towers or the like. Typically, multiple antennas are mounted on the tower, and a separate baseband unit and radio are connected to each antenna. Each antenna provides cellular service to a defined coverage area or “sector.”
FIG. 1 is a simplified, schematic diagram that illustrates a conventional cellular base station 10. As shown in FIG. 1, the cellular base station 10 includes an antenna tower 30 and an equipment enclosure 20 that is located at the base of the antenna tower 30. A plurality of baseband units 22 and radios 24 are located within the equipment enclosure 20. Each baseband unit 22 is connected to a respective one of the radios 24 and is also in communication with a backhaul communications system 44. Three sectorized antennas 32 (labelled antennas 32-1, 32-2, 32-3) are located at the top of the antenna tower 30. Three coaxial cables 34 (which are bundled together in FIG. 1 to appear as a single cable) connect the radios 24 to the respective antennas 32. Each end of each coaxial cable 34 may be connected to a duplexer (not shown) so that both the transmit and receive signals for each radio 24 may be carried on a single coaxial cable 34. In some implementations the radios 24 are located at the top of the tower 30 instead of in the equipment enclosure 20 to reduce signal transmission losses.
Cellular base stations typically use directional antennas 32 such as phased array antennas to provide increased antenna gain throughout a defined coverage area. A typical phased array antenna 32 may be implemented as a planar array of radiating elements mounted on a panel, with perhaps ten radiating elements per panel. Typically, each radiating element is used to (1) transmit radio frequency (“RF”) signals that are received from a transmit port of an associated radio 24 and (2) receive RF signals from mobile users and feed such received signals to the receive port of the associated radio 24. Duplexers are typically used to connect the radio 24 to each respective radiating element of the antenna 32. A “duplexer” refers to a well-known type of three-port filter assembly that is used to connect both the transmit and receive ports of a radio 24 to an antenna 32 or to a radiating element of multi-element antenna 32. Duplexers are used to isolate the RF transmission paths to the transmit and receive ports of the radio 24 from each other while allowing both RF transmission paths access to the radiating elements of the antenna 32, and may accomplish this even though the transmit and receive frequency bands may be closely spaced together.
To transmit RF signals to, and receive RF signals from, a defined coverage area, each directional antenna 32 is typically mounted to face in a specific direction (referred to as “azimuth”) relative to a reference such as true north, to be inclined at a specific downward angle with respect to the horizontal in the plane of the azimuth (referred to as “elevation” or “tilt”), and to be vertically aligned with respect to the horizontal (referred to as “roll”).
FIG. 2A is a perspective view of a lensed multi-beam base station antenna 200 that can be used to implement the directional antennas 32 of FIG. 1. FIG. 2B is a cross-sectional view of the lensed multi-beam base station antenna 200. The lensed multi-beam base station antenna 200 is described in detail in U.S. Patent Publication No. 2015/0091767, the disclosure of which is hereby incorporated herein by reference.
Referring to FIGS. 2A and 2B, the multi-beam base station antenna 200 includes one or more linear arrays of radiating elements 210A, 210B, and 210C (referred to herein collectively using reference numeral 210). These linear arrays of radiating elements 210 are also referred to as “linear arrays” or “arrays” herein. The antenna 200 further includes an RF lens 230. Each linear array 210 may have approximately the same length as the lens 230. The multi-beam base station antenna 200 may also include one or more of a secondary lens 240 (see FIG. 2B), a reflector 250, a radome 260, end caps 270, a tray 280 (see FIG. 2B) and input/output ports 290. In the description that follows, the azimuth plane is perpendicular to the longitudinal axis of the RF lens 230, and the elevation plane is parallel to the longitudinal axis of the RF lens 230.
The RF lens 230 is used to focus the radiation coverage pattern or “beam” of the linear arrays 210 in the azimuth direction. For example, the RF lens 230 may shrink the 3 dB beam widths of the beams (labeled BEAM1, BEAM2 and BEAM 3 in FIG. 2B) output by each linear array 210 from about 65° to about 23° in the azimuth plane. While the antenna 200 includes three linear arrays 210, different numbers of linear arrays 210 may be used.
Each linear array 210 includes a plurality of radiating elements 212. Each radiating element 212 may comprise, for example, a dipole, a patch or any other appropriate radiating element. Each radiating element 212 may be implemented as a pair of cross-polarized radiating elements, where one radiating element of the pair radiates RF energy with a +45° polarization and the other radiating element of the pair radiates RF energy with a −45° polarization.
The RF lens 230 narrows the half power beam width (“HPBW”) of each of the linear arrays 210 while increasing the gain of the beam by, for example, about 4-5 dB for the 3-beam multi-beam antenna 200 depicted in FIGS. 2A and 2B. All three linear arrays 210 share the same RF lens 230, and, thus, each linear array 210 has its HPBW altered in the same manner. The longitudinal axes of the linear arrays 210 of radiating elements 212 can be parallel with the longitudinal axis of the lens 230. In other embodiments, the axis of the linear arrays 210 can be slightly tilted (2-10°) to the axis of the lens 230 (for example, for better return loss or port-to-port isolation tuning).
The multi-beam base station antenna 200 may be used to increase system capacity. For example, a conventional 65° azimuth HPBW antenna could be replaced with the multi-beam base station antenna 200 as described above. This would increase the traffic handling capacity for the base station 10, as each beam would have 4-5 dB higher gain and hence could support higher data rates at the same quality of service. In another example, the multi-beam base station antenna 200 may be used to reduce antenna count at a tower or other mounting location. The three beams (BEAM 1, BEAM 2, BEAM 3) generated by the antenna 200 are shown schematically in FIG. 2B. The azimuth angle for each beam may be approximately perpendicular to the reflector 250 for each of the linear arrays 210. In the depicted embodiment the −10 dB beam width for each of the three beams is approximately 40° and the center of each beam is pointed at azimuth angles of −40°, 0°, and 40°, respectively. Thus, the three beams together provide 120° coverage.
The RF lens 230 may be formed of a dielectric lens material 232. The RF lens 230 may include a shell, such as a hollow, lightweight structure that holds the dielectric material 232. The dielectric lens material 232 focuses the RF energy that radiates from, and is received by, the linear arrays 210.